A D2D discovery process is a process of determining whether a D2D-enabled UE is in proximity of other D2D-enabled UE. A discovering D2D-enabled UE determines whether other D2D-enabled UE is of interest to the discovering D2D-enabled UE based on the D2D discovery process. The other D2D-enabled UE is of interest to the discovering D2D-enabled UE if proximity of the other D2D-enabled UE needs to be known by one or more authorized applications on the discovering D2D-enabled UE. For example, a social networking application may be enabled to use a D2D discovery feature. The D2D discovery process enables a D2D-enabled UE of a given user of a social networking application to discover D2D-enabled UEs of friends of the given user of the social networking application, or to be discoverable by the D2D-enabled UEs of the friends of the given user of the social networking application. In another example, the D2D discovery process may enable the D2D-enabled UE of a given user of a search application to discover stores/restaurants, and the like of interest of the D2D-enabled UE of the given user of the search application in proximity of the D2D-enabled UE of the given user of the search application.
The D2D discovery process may be implemented in various forms, and this will be described below.
The D2D-enabled UE may discover other D2D-enabled UEs in proximity of the D2D-enabled UE using direct UE-to-UE signaling. The D2D discovery process which uses the direct UE-to-UE signaling is called a D2D direct discovery process.
Alternatively, a communication network determines proximity of two D2D-enabled UEs, and informs the two D2D-enabled UEs of the proximity of the two D2D-enabled UEs. The D2D discovery process in which the communication network determines proximity of D2D-enabled UEs, and informs the D2D-enabled UEs of the proximity of the D2D-enabled UEs is called a network assisted D2D discovery process.
In the D2D direct discovery process, the D2D UE transmits discovery information on the discovery resource.
A pool of resources (i.e. a discovery resource pool) is reserved by the network for D2D direct discovery process. A TX D2D UE randomly selects a resource from the discovery resource pool, and transmits discovery information using the selected discovery resource. A RX D2D UE monitors all of discovery resources included in the discovery resource pool in order to receive the discovery information. This scheme results in collision among discovery signals which are transmitted by a plurality of TX D2D UEs. So, if the network (i.e., a base station (or an eNB) or a centralized resource coordinator) allocates a dedicated discovery resource to a TX D2D UE, the collision among the discovery signals may be avoided.
One of issues in the dedicated discovery resource allocation is how the TX D2D UE obtains resources from network. In a conventional communication network a TX D2D UE transmits a buffer status report (BSR) using medium access control (MAC) control element to a network entity (e.g. a base station or an enhanced nodeB), wherein the BSR comprises of number of bytes which the TX D2D UE wants to transmit to the network. In response to BSR, the network entity transmits a physical downlink common control channel (PDCCH) carrying control information which indicates the allocated resources. The PDCCH is masked with a radio network terminal identifier assigned to the TX D2D UE. It will be noted that this approach is not suitable for dedicated discovery resource allocation as it requires a new BSR format for discovery as a network entity should know whether the TX D2D UE needs resources for discovery or for transmission to the network. Additionally, the TX D2D UE requires a new downlink control information (DCI) format as resources for discovery are different from resources used for communication with the network. It also requires a new radio network temporary identifier (RNTI) to be assigned to the TX D2D UE to differentiate a PDCCH for discovery from the PDCCH for communication with the network. So, there is a need for a new scheme to allocate dedicated discovery resources to the TX D2D UE.
Another issue in the dedicated discovery resource allocation is that the TX D2D UE may acquire a dedicated discovery resource for transmitting the discovery signal from the base station, and the RX D2D UE has to monitor all of the discovery resources which are allocated for discovery. The discovery information which is transmitted by the TX D2D UE may be received by several RX D2D UEs. Generally, the D2D TX UE does not know which RX D2D UEs will receive the discovery information which is transmitted by the D2D TX UE.
So, upon requesting a dedicated discovery resource to the base station, the TX D2D UE cannot indicate to the base station which RX D2D UEs will receive the discovery information which is transmitted by the TX D2D UE. While allocating a dedicated discovery resource to the TX D2D UE, the base station does not know RX D2D UEs. The RX D2D UEs do not know a cell specific UE identifier (ID) of the TX D2D UE in which the RX D2D UEs are interested.
So, there is also a need for a scheme of notifying information on a dedicated discovery resource which is used by the TX D2D UE to a RX D2D UE.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.